沉淀法合成三硅酸镁粉体的孔结构及吸附性能

Porous structure and adsorption properties of magnesium trisilicate synthesised by a precipitation method

以Na2O.nSiO2和Mg(NO3)2为原料,经沉淀法合成得到三硅酸镁。采用BET、吡啶吸附和亚甲基蓝吸附等表征手段,考察了不同加料顺序和不同活化方法对样品孔道结构、表面酸性及吸附性能的影响。结果表明,滴定顺序对样品的表面织构有明显影响,Mg(NO3)2溶液滴入Na2O.nSiO2溶液合成的样品为微孔材料,主要为3 nm以下的微孔,比表面积达568.93 m2/g,孔容为0.3524 cm3/g;Na2O.nSiO2溶液滴入Mg(NO3)2溶液合成的样品为大孔材料,比表面积为179.40 m2/g,孔容为0.8350 cm3/g;各样品孔径均呈多峰分布;煅烧和酸化均可提高样品的表面酸量;各样品的亚甲基蓝吸附量与表面织构规律并不完全相同,表明孔道结构并不是影响样品吸附性能的唯一因素,酸活性位点的数量、强弱以及种类对样品的吸附性能均有一定影响。

Magnesium trisilicate was synthesized by precipitation using Na2O·nSiO2 and Mg（ NO3 ）2 as raw materials. The precipitate was heated at 450 ℃ or activated by H2SO4 , after which the samples were characterized by BET, pyridine adsorption and methylene blue adsorption to check the effect of method of mixing, calcination and acidic activation on the porous structure, surface acidity and adsorption properties. The results showed that the sam- ple which was synthesized by addition of Mg（ NO3 ）2 to the sodium silicate solution was microporous with a specific surface area of 568.93 m2/g, a pore capacity of 0. 3542cm3/g and exhibited a muhimodal pore width distribution in the 1 - 3 nm and 0. 7 - 0. 9 nm micropore regions. The sample which was synthesized by addition of the sodium sili- cate solution to Mg（ NO3 ）2 solution was mesoporous with a specific surface area of 179.40 m2/g and a pore capacity of 0. 8350 cm3/g. Calcination and acidic activation increased the surface acidity, reduced the specific surface area and changed the distribution of pore width. The porous structure and the quantity, type and strength of surface acidity all affect the adsorption properties of the material.